Circuits to precisely control, drive, and regulate brushless DC (BLDC) electric motors are required in many applications. These circuits often create pulse-width modulated (PWM) drive signals that are used to control power to the motor.
As is known, BLDC motors may include multiple coils. These coils, when energized, cause the motor to turn. However, in order for the motor to continuously turn, a motor controller circuit may have to energize one or more (but not all) of the coils at a time, energize the coils in a particular order, energize the coils in a forward and backward direction at different times, etc. The periods of time in which the coils are energized are often referred to as so-called “phases” of the motor.
The sequence and timing of which coils are energized is dependent upon the design of the BLDC motor. As an example, a particular BLDC motor may have three coils that must be energized in sequence, i.e. a round-robin fashion, in order to turn the motor. Such a motor may have three “phases.” In each phase, a different one or more of the three coils is energized. As the motor turns, the phase will change, and the motor driver will energize the next one or more coils in order to keep the motor spinning.
Some known electric motor drive circuits are described in U.S. Pat. No. 7,590,334, issued Sep. 15, 2009; U.S. Pat. No. 7,747,146, issued Jun. 29, 2010, U.S. patent application Ser. No. 13/271,723, filed Oct. 12, 2011; and U.S. patent application Ser. No. 13/595,430, filed Aug. 29, 2012, each of which is incorporated here by reference, and each of which is assigned to the assignee of the present invention.
In certain motor applications, it is desirable to minimize motor jitter, i.e. an undesired deviation from true periodicity of an assumed periodic signal of the motor. In other words, jitter may be a tendency for the motor speed, or a signal representing the motor speed, to inadvertently or unexpectedly change or fluctuate. Jitter can be caused by various stimuli. For example, an incomplete or short pulse (i.e. a pulse with a shorter than normal duration) on a PWM drive signal can cause the amount of power applied to the motor to fluctuate, and thus cause the speed of the motor to fluctuate.
In view of the above, it would be desirable to provide a motor control circuit and associated method that can reduce the occurrence of motor jitter.